The present invention is an improvement on the solar heating panel described in an earlier Canadian patent, Pat. No. 1,069,006, which issued Jan. 1, 1980.
Such patent teaches a solar heating panel comprising a top transparent sheet, the transparent sheet having a plurality of mutually adjacent parallel raised semi-tubular portions shaped to reflect a portion of the incident energy from the sun to adjacent portions, the transparent sheet overlying and being affixed to a dark opaque sheet to thereby form hollow areas intermediate each of the semi-tubular portions on the top transparent sheet, through which a heat-absorbing medium may flow.
In the prior art solar panels described above, the top transparent sheet intermediate the upwardly protruding or raised semi-tubular portions thereon contacts the opaque bottom member, and glue, adhesive or hot-melt sealant is used at such contact points or "glue lines" to affix the top transparent sheet to a flat bottom opaque sheet, and effectively sealingly partition one flow channel from the other.
This method is commonly used in other prior art devices, particularly where top and bottom sheets of a polytetrafluorethylene plastic or PVC material are used, as may be seen from U.S. Pat. Nos. 4,151,830 to Crombie et al; 4,476,855 to Benfield; 4,471,759 to Andersen et al and French Pat. No. 2,569,259 to Stref.
In order to effectively sealingly affix the top sheet to the bottom sheet during construction of the solar panel, it is necessary that the glue, when first applied in its unhardened state, or the melted material arising from a heat sealing process, remain along the glue line for a sufficient length of time to allow hardening of the glue or heated material, to thereby bond the top sheet to the bottom sheet. Frequently, in the prior art designs, because of the action of gravity and the particular configuration of the two sheets to be joined, the glue or melted material in its unhardened state would flow away from the glue line, which accordingly resulted in an ineffective sealing engagement along the glue lines due to absence of adhesive or melted product at certain locations. Accordingly, the concave depressions intermediate each of the raised convex portions on the bottom sheet member of the present invention act as glue receptacles to retain the glue in the desired position, and thereby overcome the above problem of prior art designs.
A further problem encountered with prior art designs was evident when applying the glue or adhesive to the bottom sheet member or top sheet member. A worker who was operating a glue dispensing device had to manually guide the glue-dispensing tip of the glue dispenser in a straight line along either the top or bottom member to apply the glue to such members. Frequently, this was difficult to accomplish and any inexperience of the worker resulted in "wavy" glue lines, and thus poor sealing between the top and bottom sheet members. With a configuration of the present invention, wherein the bottom sheet member has a plurality of depressions intermediate each of the raised convex portions thereon, these depressions which receive the adhesive further act as a guide for the glue dispensing tip of the glue dispensing device. Accordingly, a worker assembling the top sheet member to the bottom sheet member need only roughly guide the glue dispensing device along each of the depressions. The glue is then linearly dispensed along the glue line, and the mating half of the top sheet member, when the top and bottom sheet are placed in mutual overlying relation, is automatically positioned along the glue line, and a proper seal is obtained.
A still further problem encountered with the prior art configurations, particularly where a heat sealing method was used, was that the configuration of the top sheet member and the bottom sheet member did not permit self-alignment when the top sheet and bottom sheet members were brought into abutting contact. Accordingly, misalignment of the top and bottom sheet members sometimes occurred, resulting in ineffectual sealing engagement of the two members.
Also, to achieve the desired qualities in the top and bottom sheets of low weight and low cost, the top sheet member and bottom sheet member are normally comprised of a substantially rigid plastic material. Accordingly, such materials were susceptible to bending under certain conditions. A further problem then arose with the prior art configurations in that the bottom sheet members of the solar panels were not shaped to resist bending caused by fluid pressure within the flow channels. Thus, the working medium fluid pressure within the flow channels would frequently cause the bottom sheet member to bulge slightly under such pressure, particularly where a thin, flat thermoformed plastic material was used for the bottom sheet member. This bulging condition induced cracks in the glue line joining the top sheet to the bottom sheet, since the bulging of the bottom sheet caused the bottom sheet to pull away from the top sheet along the glue line by attacking glue adhesive peel strength. Accordingly, a serious problem of earlier panels was that separation of the bottom sheet member from the top sheet member along a single glue line was frequently sufficient to cause immediate domino-like separation of the bottom sheet from the top sheet along remaining glue lines. Consequently, rupture of the panel occurred when the remaining glue lines were then unable to withstand the increased separation force thereon. PG,7
Also, even if the remaining glue lines were of sufficient strength to maintain the top and bottom sheet members adhered to one another, where one or more glue lines ineffectively sealed one flow passage from another, undesirable mixing of fluid between adjacent flow passages resulted. This resulted in loss of thermal efficiency, and also, at times, leakage of the working medium from the solar panel itself. Frequently, when such solar panels were positioned vertically, the hydrostatic pressure of the working medium itself, particularly if water was the working medium employed, was sufficient in itself without any added pump pressure to cause bending of the bottom sheet to such a degree that the bottom sheet member was pulled away from the glue line.
Thus a real need existed for a solar panel having working medium flow passages that were of a configuration that allowed easy and more solid gluing along the glue lines. A need further existed for flow passages having a configuration capable of withstanding greater pressures to reduce or eliminate bending of the bottom sheet which resulted in the bottom sheet pulling away from the top sheet member with the consequential loss of sealing engagement along the glue lines.